1. Field of the Invention
The present invention relates to an inkjet recording head, an inkjet recorder employing the same, a process for producing the recording head, a fluorine-containing polymerizable polymer, and a polymerizable composition for forming a water-repellent resin film. More particularly, the invention relates to a recording head in which the periphery of ink discharging holes have undergone an ink-repellent treatment and are excellent in water repellency and wearing resistance and with which printed images of excellent quality can be obtained.
2. Background Art
Inkjet recorders in which an ink (or recording liquid) is discharged from discharge holes of a recording head are known as recorders excellent in silence, high-speed recording, etc. The quality of images obtained with a recording head considerably depends on the positional precision of the dots formed from ink droplets on the recording paper. This positional precision of dots is influenced by the direction of flight of ink droplets discharged from discharge holes of the recording head. A technique effective in keeping the direction of flight constant is to regulate the periphery parts of the discharge hole so as to be even and stable during ink droplet ejection. Specifically, it is effective to conduct a treatment for imparting water repellency (ink repellency) to recording head surfaces including the periphery parts of the discharge hole. Furthermore, in the case where a foreign matter such as an ink or paper adheres to the periphery parts of the discharge hole, which have undergone a water-repellent treatment, the foreign matter is removed by scrapping with a cleaning member, e.g., a blade. In this case, the parts which have undergone a water-repellent treatment are required to have resistance to the ink or chemical ingredients contained therein and resistance to the friction caused by a rubbing operation, etc.
A technique for a water-repellent treatment is to treat the periphery parts of discharge hole of a recording head with a fluoroalkylalkoxysilane or the like to impart water repellency thereto (see, for example, JP-A-56-89569). However, this technique has a drawback that for perfectly conduct the treatment, it is necessary to treat the periphery parts of the discharge hole in a manner which may destroy the material constituting the discharging holes. For example, the peripheral parts should be heated at a temperature as high as 150° C. or above for a prolonged time period or heated in a high-pH solution. In addition, the peripheral parts thus treated are still insufficient in resistance to friction in, e.g., a wiping operation.
Another technique for a water-repellent treatment which has been proposed comprises using a fluorine compound having a reactive group in combination with an epoxy resin in order to form through polymerization a film containing the fluorine compound fixed therein and thereby obtain high water repellency even after cleaning operations (see, for example, JP-A-7-148930) However, since the fluorine compound is less apt to dissolve in epoxy resins, it is often difficult to evenly conduct the treatment. In case where the fluoroalkyl chain of the fluorine compound is shortened in order to enhance solubility, the fluoroalkyl chains show impaired migration to the surface, resulting in poor water repellency. Furthermore, use of such a fluorine compound gives a crosslinked film containing an increased amount of the fluoroalkyl chains or having a reduced crosslink density, resulting in a reduced film strength and impaired durability.
There also is a technique in which treatment is conducted with a treating agent comprising a fluorine-containing resin and a blocked isocyanate (see, for example, Japanese Patent No. 3,382,416). High frictional resistance has been reported to be attained by this technique. However, since the blocked isocyanate has poor reactivity, this technique had had a problem that the treatment should be conducted at a high temperature (160° C.) for a prolonged time period and this may destroy the head-constituting material as in the case described above. Consequently, it has been difficult to obtain an increased crosslink density and produce a coating film having excellent performance with satisfactory reproducibility.
Furthermore, there is a technique in which water repellency is imparted by forming a film of a polymer having fluorine-containing polymer chains which have gathered so as to form physical aggregates (see, for example, JP-A-2001-233972). High water repellency has been reported to be attained by this technique. However, it is necessary to increase the amount of a reactive group, such as epoxy or hydroxy, for crosslinking the polymer, and this necessarily results in a hydrophilized cured film. Consequently, it has been difficult to reconcile strength and water repellency.
On the other hand, a resin which comprises a fluorine-containing block copolymer and cures with actinic energy rays has been proposed (see, for example, Japanese Patent No. 3.021,746). The copolymer which has been proposed has excellent water repellency. However, in applications where this copolymer comes into contact with inkjet inks which contain a solvent and a surfactant, have a low surface tension, and are alkaline, the long-term retention of water (ink) repellency and high frictional resistance has been limited.
To sum up, none of the inkjet recording heads according to the related-art techniques which have been proposed so far reconciles wearing resistance and water repellency (ink repellency) to a desired level. There is hence a desire for the development of an inkjet recording head which is excellent not only in water repellency but in long-term wearing resistance and attains high printed-image quality.